MS01-026: Superfluous Decoding Operation Can Allow Command Execution Through IIS (295534)


The information in this article applies to:

  • Microsoft Internet Information Services 5.0
  • Microsoft Internet Information Server 4.0
This article was previously published under Q295534

SYMPTOMS

A vulnerability exists in Microsoft Internet Information Services (IIS) 5.0 and Microsoft Internet Information Server (IIS) 4.0 that can enable a malicious user to run (execute) operating system commands on an affected Web server. This gives the malicious user the ability to modify Web pages, add, change, or delete files, reformat the hard disk, or take other actions (such as uploading any code to the server and running it).

Best practices, if followed, can make it difficult or impossible for an attacker to exploit the vulnerability. Even if an attacker successfully exploits it, the vulnerability does not grant the attacker administrative control over the server. Instead, the vulnerability grants the attacker privileges that are normally reserved for a user who can log on to the server interactively. Nevertheless, even these privileges can enable a malicious user to cause widespread damage and allow a point from which the malicious user can launch additional attacks in the hope of gaining additional privileges.

Mitigating Factors:
  • This vulnerability does not provide a way for the attacker to learn the folder structure on the server. As a result, if the operating system is installed on a separate drive from the Web root or in non-standard folders, it can prevent an attacker from locating programs of interest.
  • This vulnerability does not provide administrative access to the server. If you followed the recommendations in the IIS 4.0 and IIS 5.0 security checklists, sensitive programs are moved to folders that only the administrator can access, and non-administrative access to server resources is severely restricted.

CAUSE

This vulnerability occurs because of an error in the functionality that processes requests to run programs that are housed on the server. A superfluous decoding operation could give an attacker the opportunity to bypass security checks and escape the server's virtual folder structure, thereby enabling the attacker to run operating system commands on the server.

RESOLUTION

For additional information on what is fixed by the following patches, click the article number below to view the article in the Microsoft Knowledge Base:

297860 IIS 5.0 Security and Post-Windows NT 4.0 SP5 IIS 4.0 Patch Rollup

Internet Information Services 5.0

To resolve this problem, either obtain the hotfix referenced in this section or Windows 2000 Security Rollup Package 1 (SRP1). For additional information about SRP1, click the article number below to view the article in the Microsoft Knowledge Base:

311401 Windows 2000 Security Rollup Package 1 (SRP1), January 2002

To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

260910 How to Obtain the Latest Windows 2000 Service Pack

The following file is available for download from the Microsoft Download Center:

DownloadDownload Q293826_W2K_SP3_x86_en.exe now

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English version of this fix should have the following file attributes or later:
   Date        Time    Version        Size     File name
   --------------------------------------------------------
   05/04/2001  11:48a  5.0.2195.3407  245,520  Adsiis.dll
   05/04/2001  11:48a  5.0.2195.3407  332,560  Asp.dll
   08/26/2000  06:30p                   6,512  Fixerr.js
   11/10/2000  11:21p  5.0.2195.3407  593,976  Fp4autl.dll
   03/27/2001  10:10p  5.0.2195.3407  445,712  Httpext.dll
   05/04/2001  11:48a  5.0.2195.3407   56,592  Httpodbc.dll
   05/04/2001  11:48a  5.0.2195.3407  122,640  Iisrtl.dll
   05/04/2001  11:48a  5.0.2195.3407   13,584  Infoadmn.dll
   05/04/2001  11:48a  5.0.2195.3407  245,520  Infocomm.dll
   05/04/2001  11:48a  5.0.2195.3407   62,736  Isatq.dll
   05/04/2001  11:48a  5.0.2195.3407   46,352  Ism.dll
   05/04/2001  11:48a  5.0.2195.3407   76,560  Msw3prt.dll
   10/17/2000  01:38p  5.0.2195.3407    6,928  Schmupd.exe
   05/04/2001  11:48a  5.0.2195.3407   41,232  Ssinc.dll
   05/04/2001  11:48a  5.0.2195.3407    7,440  W3ctrs.dll
   05/04/2001  11:48a  5.0.2195.3407  357,648  W3svc.dll
NOTE: You can install this patch on systems that are running Microsoft Windows 2000 Gold, Windows 2000 Service Pack 1, or Windows 2000 Service Pack 2.

Internet Information Server 4.0

To resolve this problem, obtain the Windows NT 4.0 Security Rollup Package. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

299444 Post-Windows NT 4.0 Service Pack 6a Security Rollup Package (SRP)

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that you determine are at risk of attack. Evaluate the computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to the computer. See the associated Microsoft Security Bulletin to help determine the degree of risk. This hotfix may receive additional testing. If the computer is sufficiently at risk, we recommend that you apply this hotfix now.

To resolve this problem immediately, download the hotfix by following the instructions later in this article or contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Note In special cases, charges that are ordinarily incurred for support calls may be canceled, if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question. The following file is available for download from the Microsoft Download Center:

DownloadDownload Q295534i.exe now
NOTE: Q295534is.exe are the Symbols files.

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English version of this fix should have the following file attributes or later:
   Date        Time    Version        Size     File name     Platform
   ------------------------------------------------------------------
   04/11/2001  01:32p  4.2.764.1      214,544  Adsiis.dll    x86
   04/11/2001  01:33p  4.2.764.1      330,672  Asp.dll       x86
   04/02/2001  04:55p  4.0.2.4701     593,976  Fp4autl.dll   x86
   04/11/2001  01:32p  4.2.764.1       81,888  Ftpsvc2.dll   x86
   04/11/2001  01:32p  4.2.764.1       55,392  Httpodbc.dll  x86
   04/11/2001  01:32p  4.2.764.1       98,912  Iischema.dll  x86
   04/11/2001  01:31p  4.2.764.1       63,472  Iislog.dll    x86
   04/11/2001  01:31p  4.2.764.1      185,792  Infocomm.dll  x86
   04/11/2001  01:31p  4.2.764.1       29,520  Iscomlog.dll  x86
   04/11/2001  01:35p  4.2.764.1       54,560  Ism.dll       x86
   04/02/2001  04:55p  4.0.1381.7086  375,056  Kernel32.dll  x86
   04/11/2001  01:36p  4.2.764.1        9,680  Schmupd.exe   x86
   04/11/2001  01:32p  4.2.764.1       38,256  Ssinc.dll     x86
   04/11/2001  01:32p  4.2.764.1       25,360  Sspifilt.dll  x86
   04/11/2001  01:32p  4.2.764.1      229,024  W3svc.dll     x86
   04/11/2001  01:31p  4.2.764.1       88,032  Wam.dll       x86

   08/20/1999  12:26a  4.0.1381.321   171,280  W3svc.dll     Alpha
NOTE: You can install this patch on systems that are running Microsoft Windows NT 4.0 Service Pack 5 or Windows NT 4.0 Service Pack 6a.

Windows NT Server version 4.0, Terminal Server Edition

To resolve this problem, obtain the Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package (SRP). For additional information about the SRP, click the article number below to view the article in the Microsoft Knowledge Base:

317636 Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package

STATUS

Internet Information Services 5.0

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Internet Information Services 5.0. This problem was first corrected in Windows 2000 Service Pack 3.

Internet Information Server 4.0

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Internet Information Server 4.0.

MORE INFORMATION

For additional information about how to obtain a hotfix for Windows 2000 Datacenter Server, click the article number below to view the article in the Microsoft Knowledge Base:

265173 The Datacenter Program and Windows 2000 Datacenter Server Product

For additional information about how to install multiple hotfixes with only one reboot, click the article number below to view the article in the Microsoft Knowledge Base:

296861 Use QChain.exe to Install Multiple Hotfixes with One Reboot

For more information on this vulnerability, see the following Microsoft Web site:

http://www.microsoft.com/technet/security/bulletin/ms01-026.mspx

Modification Type:MinorLast Reviewed:10/13/2006
Keywords:kbHotfixServer kbQFE kbbug kbfix kbgraphxlinkcritical KbSECHack kbSecurity KbSECVulnerability kbWin2000PreSP3Fix kbWin2000sp3fix KB295534
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